1. Field of Invention
This invention relates to a barium titanate-based dielectric composition, and more particularly to a barium titanate-based dielectric composition that can be used to form multilayer ceramic chip capacitors having internal base metal electrodes formed of nickel or nickel alloys.
2. Background of the Invention
Multilayer ceramic chip capacitors have been widely utilized as miniature-sized, high capacitance, and high reliability electronic components. In accordance with increasing demands for high-performance electronic equipment, multilayer ceramic chip capacitors also have encountered marketplace demand for smaller size, higher capacitance, lower cost, and higher reliability.
Multilayer ceramic chip capacitors generally are fabricated by forming alternating layers of an internal electrode forming paste and a dielectric layer-forming paste. Such layers are typically formed by sheeting, printing, or similar techniques, followed by concurrent firing.
Generally, the internal electrodes have been formed of conductors such as palladium and palladium alloys. Although palladium is expensive, it can be partially replaced by the use of relatively inexpensive base metals such as nickel and its alloys. A “base metal” is any metal other than gold, silver, palladium, and platinum. Base metal internal electrodes can become oxidized if fired in ambient air, so the dielectric layers and internal electrode layers must be co-fired in a reducing atmosphere. Firing in a reducing atmosphere, however, causes the dielectric layers to be reduced, which decreases resistivity. Multilayer ceramic chip capacitors using non-reducible dielectric materials have been proposed, however, such devices typically have a shorter life of insulation resistance (IR) and low reliability.
When the dielectric material is subject to a DC electric field, its relative dielectric constant (K) decreases with time. If thinner dielectric layers are used in order to provide chip capacitors of a smaller size and greater capacitance, application of DC voltages across the capacitor causes the dielectric layers to receive a more intense electric field, resulting in a greater change of dielectric constant with time, that is, a greater change of capacitance with time. Such changes are undesirable in most applications.
The Electronic Industry Association (EIA) prescribes a standard for the temperature coefficient of capacitance (TCC) known as the Y5V characteristic. The Y5V characteristic requires that the change of capacitance be within +22% and −82% of its value at the reference temperature, 25° C., over the temperature range −30° C. to 85° C.